Regulated hydraulic drive

ABSTRACT

A HYDRAULIC COMPRISES A COMBUSTION ENGINE, A HYDRAULIC TRANSMISSION WHOSE PUMP IS DRIVEN BY THE ENGINE, AND A REGULATING APPARATUS INCLUDING AN AUXILIARY PUMP DISCHARGING THROUGH A MAIN CONDUIT, WHOSE PRESSURE IS REGULATED BY A PRESSURE-REGULATING VALVE UNDER THE CONTROL OF AN OPERATOR, AND THROUGH TWO VARIABLE THROTTLES WHOSE THROTTLE CROSS-SECTIONS ARE SIMULTANEOUSLY INCREASED AND DECREASED, RESPECTIVELY, BY THROTTLE CONTROL MEANS RESPONSIVE TO THE PRESSURE IN THE TRANSMISSION PUMP. THE DIFFERENT THROTTLED PRESSURES ARE APPLIED TO A FIRST SERVO MOTOR CONTROLLING THE ROTARY SPEED OF THE COMBUSTION ENGINE, AND TO A SECOND SERVO MOTOR CONTROLLING THE TRANSMISSION PUMP TO VARY THE PISTON STROKE AND OUTPUT OF THE SAME. WHEN THE OPERATOR ADJUSTS THE PRESSURE-REGULATING VALVE, THE TRANSMISSION MOTOR OPERATES AT DIFFERENT ROTARY SPEEDS, AND ANY SELECTED ROTARY SPEED IS MAINTAINED BY THE REGULATING APPARATUS CONSTANT AND INDEPENDENT OF THE LOAD, WHILE THE REGULATED HYDRAULIC DRIVE OPERATES AT OPTIMAL EFFICIENCY.

Oct. 5, 1971 w. KOBALD 3,609,964

REGULATED HYDRAULIC DRIVE Filed April 14, 1970 2 Sheets-Sheet 1 IN VEN TOR. Walfer K OBAL D Oct. 5, 1971 w. KOBALD v 3,609,964

REGULATED HYDRAULIC DRIVE Filed April 14, 1970 2 Sheets-Sheet 73 IN V EN TOR. Walter K 08A L D U.S. CI. 60-19 United States Patent Oflice 3,609,964 Patented Oct. 5, 1971 REGULATED HYDRAULIC DRIV Walter Kobald, Stuttgart-Feuerbach, Germany, assignor to Robert Bosch, G.m.b.H., Stuttgart, Germany Filed Apr. 14, 1970, Ser. No. 28,424

Claims priority, application Germany, Apr. 24, 1969, P 19 20 859.4 Int. Cl. F02b 73/00 14 Claims ABSTRACT OF THE DISCLOSURE A hydraulic drive comprises a combustion engine, a hydraulic transmission whose pump is driven by the engine, and a regulating apparatus including an auxiliary pump discharging through a main conduit, whose pressure is regulated by a pressure-regulating valve under the control of an operator, and through two variable throttles whose throttle cross-sections are simultaneously increased and decreased, respectively, by throttle control means responsive to the pressure in the transmission pump. The different throttled pressures are applied to a first servo motor controlling the rotary speed of the combustion engine, and to a second servo motor controlling the transmission pump to vary the piston stroke and output of the same. When the operator adjusts the pressure-regulating valve, the transmission motor operates at different rotary speeds, and any selected rotary speed is maintained by the regulating apparatus constant and independent of the load, while the regulated hydraulic drive operates at optimal efliciency.

BACKGROUND OF THE INVENTION The German Pat. 1,204,569 discloses a regulated hydraulic drive with a regulating apparatus which is, on the one hand controlled by the foot pedal determining the rotary speed of the prime mover combustion engine, and, on the other hand, is controlled by the pressure prevailing in the hydrostatic transmissionwhose pump is driven by the combustion engine.

The apparatus of the prior art permits it to operate the combustion engine and the hydrostatic transmission in a range of high efficiency. However, a great number of regulating devices and control valves are necessary, so that the hydraulic drive of the prior art is very expensive. Another disadvantage is that centrifugal governors are used for regulation which are unreliable in the lower speed range.

SUMMARY OF THE INVENTION 1 It is one object of the invention to provide a regulated hydraulic drive with a simple regulating apparatus which effects an operation of the drive within the range of optimal efliciencies.

pressure medium under constant pressure which is divided into two branch streams respectively fiowing through first and second throttles. The first throttles are of equal and constant throttle cross-section, while the second throttles have throttle cross-sections which are variable and are simultaneously varied by control means responsive to the pressure in the hydrostatic transmission. One of the branch streams controls the supply of fuel to the combustion engine, and the other controls the stroke of the transmission pump.

A regulating apparatus according to a preferred embodiment of the invention includes a source of pressure medium, such as an auxiliary pump, conduit means including a main conduit receiving the medium from the source and first and second branch conduits, first hydraulic operating means communicating with the first branch conduit and operatively connected with the first control means for operating the same, second hydraulic operating means communicating with the second branch conduit and operatively connected with the second control means for operating the same, a first throttle means communicating with the first branch conduit, a second throttle means communicating with the second branch conduit, a throttle control means for varying the throttle cross-sections of the first and second throttle means, and throttle operating means operatively connected with the throttle control means and hydraulically connected with the hydrostatic transmission for operating the throttle control means in response to the pressure in the hydrostatic transmission. Operator-controlled means preferably including a pressure-regulating valve in the main conduit, are provided for producing selected pressures in the main conduit so that in every position of the operator-controlled means, a different rotary speed is maintained constant and independent of the load variations of the hydraulic motor, while the engine and hydraulic transmission operate at optimal efiiciency.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view illustrating a regulated by draulic drive according to the invention;

FIG. 2 is a fragmentary schematic view illustrating a regulating apparatus used in the drive of FIG. 1;

FIG. 3 is a fragmentary schematic view illustrating a modified throttle control means; and

FIG. 4 is a diagram graphically illustrating speed variations of the prime mover engine over the ratio of the hydrostatic transmission.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, a diesel motor 1 serves as prime mover and has a first control means 2 which can be adjusted to vary the speed of the output shaft of the combustion engine 1 which is schematically indicated by the number of revolutions n of the output shaft of the combustion engine 1. The output shaft is connected with the input shaft of a hydraulic pump 3 which consequently also rotates at the rotary speed in. Hydraulic pump 3, which is preferably an axial piston pump with a Wobble plate, drives a corresponding hydraulic motor 4 whose output shaft has n revolutions. The Wheels of the vehicle, not shown, are driven by hydraulic motor 4 at n revolutions per minute. A regulating apparatus, which is illustrated in detail in FIG. 2, has an operator-controlled means 6, preferably a foot pedal, which influences the regulating apparatus 5, which is also influenced by the pressure p prevailing in the hydrostatic transmission 3, 4, and more particularly in the pump 3. The regulating ap- 3 paratus is connected with the first control means) O f 'thecor'nbu's'tion en'gine'l for" varying the rotary speed In and also connected with second control means 7 for varying the length of the piston stroke and the output of the pump 3 which drives hydraulic motor 4 accordingly.

Referring now to FIG. 2, which illustrates schematical ly the regulating apparatus 5, an auxiliary pump 8 is provided as part of the regulating apparatus, and pumps a pressure medium into a main conduit 9, 12 which is connected with a conduit 10 in which a pressure regulating valve 11 is located which is controlled by the foot pedal 6, or other adjusting means controlled by the driver of 'the vehicle. Auxiliary pump 8 pumps the pressure medium 'out of container means 35 into which also conduit 10 discharges,

Pressure medium flowing through main conduit 9, 12

" at a pressure p which is constant for each adjusted posi- 'tion of the pressure-regulating valve 11. The pressure medium flows from main conduit 12 into two branch conduits 13 and 13" in which throttles 14 and 14 are provided which have the same throttle cross-section F.

Downstream of the constant throttles 14 and 14', the pressures p and p prevail which correspond to the pressure p selected by the operator by correspondingly placing the foot pedal 6. Branch conduit 13 communicates with a conduit 20 leading to a first hydraulic operating means shown to be a servo motor having a cylinder 21, a piston 23, and a spring 22 urging piston 23 -to oppose the pressure medium'flowing from conduit 20 into cylinder 21. Piston 23 is mechanically connected with the first control means 2, see FIG. 1, by which the speed "inder 16. Piston 18 is connected with second control means 7 by which the stroke of I output, is adjusted.

The end of conduit 20 remote from cylinder 21 is pump 3, and thereby its shown in axial section, and has a throttle opening 24. The end of conduit remote from cylinder 16 is shown -'in axial section and has a throttle opening '19confronting throttle opening 24 and being aligned with the same.

"Throttle openings 24 and 19 are spaced a predetermined distance. A throttle control member 25 has a central cylindrical portion guided in a guideway 26 for longitudinal movement, and has two conical end portions 27 and 28 WhlCh respectively project into throttle openings 24 and 19, forming annular throttle cross-sections F and F in i the same. When throttle control member 25 i displaced in guideway 26 into throttle opening 24, the'thro'ttle crosssection F is decreased, and the throttle cross-section F is increased. During opposite movement of throttle control member 25, throttle cross-section F is decreased, and" throttle cross-section F is increased so that the two throttles are always simultaneously operated and adjusted. An arm 30 passes through a cut-out in the guideway 26 to throttle control member 25. Arm 30 is fixedly secured .snthat th.. .il11:9 .1 openin s 2.4 and 12ers, heat d. in?

plane. A throttle control member 36 has the form of a non-circular plate whose peripheral edge crosses throttle openings 24 and 19, reducing the free throttle cross-sections F and F Throttle-co n'tr'ol member 36 is turned about a shaft 38 by'throttle-operating means including a cylinder 37, corresponding to cylinder 33 a piston 37a connected with throttle-control member 36. The pressure medium is supplied throughconduits 35'. frornth pump 3 into cylinder 37. In accordance with variations of the pressure p in the hydrostatic transmission 3, 4,

"throttle-control member 36 is turned to increase the free flow cross-section F when the free flow cross-section F is reduced, and vice versa.

- OPEliATlON The operator or driver of a vehicle displaces the adjusting means 6, suchas' a foot pedal, so that the pressureregulating'valve 11 determines apressure p in conduit 12 on which the speed of the vehicle depends whose wheels are driven by'the hydraulic motor' 4. The displacement of the foot pedal 6 is proportional to the vehicle speed V and to the number of revolutions n of hydraulic ,motor 4. For each position of the foot pedal, a different constant pressure p and a different number of revolut ions n is obtained. Excess pressurei medium discharged through the throttle openings 24 and 19, and by the pressure-regulating valve ll fiow into container means; "which is connected with the" suction inlet of the auxil ary pump 8 so that the pressure medium circulated by tli e Regulating apparatus controls the speed n and, de-

pending on any selected position of the foot pedal 6 and on the pressure'p in' the hydrostatic transmission3, 4; the transmission ratio i of the hydrostatic transmission 3, '4, and the number of revolutions n of. the combustion engine 1 are adjusted to values at which combustion engine 1 and the hydrostatic transmission operate at optimal efficiency. At the same time, theregulating apparatus of FIG. 2 must also assure that, while optimal elficiency is maintained, the selected vehicle speed V remains constant even if the vehicle encounters resistance, and the .load on the hydraulic motor 4 ,varies. This can be'obtained when the regulating graph has the shape .of a hyperbola. I I t As shown in FIG. 4, the-abscissa represents the transmission ratio i of the hydrostatic transmission 3, 4, and the ordinate represents the number of revolutions n; of the combustion engine 1, and of the pump 3. Each position s of the foot pedal 6 is associatedwith a dilfei'ent hyperbolic regulating graph some of which are shown in FIG. 4. The regulation is obtained in the following manner The auxiliary pump 8, or any other source of a pressure medium, such as an accumulator, which need not be driven in synchronism with the combustion. engine or to a piston rod 31 of a piston 32 of a throttle-operating means which includes a spring 33 urging piston 32 to the 1 rightas'viewed in FIG. 2 against the pressure of the pressure medium supplied through a conduit 35 from the transmission pump 3 at a pressure p. When the pressure p In the embodiment of FIG. 3, the conduits 15 and 20' are connected with the branch conduits 13 and 13 as explained above for conduits 20 and 15, but are paralleltransmissiompumps a pressure mediuminto. the main conduit 9,. 10, 12. .The pressure medium inconduit 12 flows into the two branch conduits 13 and 13-",- and each of the branch streams'of the pressure medium 'fiowsthrough .the identical throttles 14, 14 having the throttle crosssection F, so that the pressure'of therespective branch streams p and p are accordingly reduced.

The pressure medium in .branch conduit 13 flows through conduit 20 and through the free throttle crosssection F into the container 35, and the same is .the'case with the pressure medium in branch conduit13 which flows through the free throttle cross-'sectionF intoxcontainer 35. The throttle cross-sectionsF and F are increased or reduced, depending on the position-of throttle control member25 which is displaced in accordance with the pressure in the throttle-operating means'32, 33' to which pressure fluid is supplied at a pressure pi frornthe hydrostatic transmissiom-A pressure p is produced in branch conduit 13, and thepressure p' is'produ'cedrin branch conduit 13'. Pressure p acts on servo motor 21, 22, 23 so that piston 23 operates the control means 2 of combustion engine 1, influencing the number of revolutions it, of the output shaft of combustion engine 1, and of the input shaft of pump 3. The pressure p acts in the cylinder 16 of the servo motor 16, 17, 18 so that piston 18 is displaced accordingly, and adjusts control means 7 by which the piston stroke of the pump 3 is adjusted, for example by tilting the Wobble plate of an axial piston pump. The pressure p of the fluid circulating in the hydrostatic transmission, is supplied to the cylinder 33 of the throttle-operating servo motor 32, 33, 34.

As a result, the pressure p is proportional to the number of revolutions and to the rotaryspeed n of the combustion engine and of pump 3, while the pressure p is proportional to the transmission ratio i of the hydrostatic transmission 3, 4. The speed V of the vehicle driven by hydraulic motor 4 is proportional to the product of the number of revolutions of combustion engine 11 and the transmission ratio i of the hydrostatic transmission 3, 4. It follows that V is proportional to p -p This means that for a selected speed of the vehicle, which should be constant, and in the event of variations of the pressure p and p during regulation, the system of coordinates shown in FIG. 4 will show a hyperbolic graph.

This may be mathetically expressed as follows:

VF p p. pm-Pm=, 2

F F i- 1 35+ 1 which represents a hyperbola with p and p as variables while K is a constant factor. The vehicle speed V varies with the pressure 12;; which is obtained by displacing foot pedal 6 and adjusting pressure-regulating valve 11. F is the throttle cross-section of throttles 14 and 14, F is the annular throttle cross-section of throttle 24, 27, and F is the throttle cross-section of throttle 19,28.

If the vehicle speed V is to be constant, the following equation is valid:

From this equation the function F :f(F can be determined. Due to the thus obtained optimal efficiency, a 'saving of fuel supplied to the combustion engine 1 is obtained.

In the modification of FIG. 3, the peripheral shape of the throttle control member 36 is selected so that the throttle cross-sections F and F are determined in accordance with the required'mathematical conditions. In the embodiment of FIG. 2, the throttle control member 25 has conical end portions slanted at different angles for obtaining the required relationship between the throttle cross-sections F and F In both embodiments, the pressure p and p depend on the free area of the throttle cross-sections.

The conduits are shown in FIG. 2 in a schematic manner, and it will be understood that the conduits can be constructed as channels and bores in the walls of a regulator casing, in which the throttles and the pressure-regulating valve 11 are provided.

In the above description, it was assumed that hydraulic motor 4 cannot be adjusted. If hydraulic motor 4 is adjustable, and has a tiltable wobble plate, for example, a hydraulic servo motor operating the wobble plate is hydraulically connected with the main conduit 12 in which a constant selected pressure prevails.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of regulated hydraulic drives differing from the types described above.

While the invention has been illustrated and described as embodied in a regulating apparatus for a hydraulic drive provided with two regulating throttles controlled by the pressure of the transmission pump, and controlling the speed'of the prime mover and the output of the transmission pump, it is not intended to be limitedto the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. Regulated hydraulic drive comprising a prime mover engine having first control means for varying the speed of said engine; a hydrostatic transmission including a hydraulic pump driven by said engine, and a hydraulic motor driven by said pump, said transmission having second control means for varying the output of said pump whereby the speed of said hydraulic motor is varied; a regulating apparatus including a source of a pressure medium, conduit means including a main conduit receiving said medium from said source and first and second branch conduits. first hydraulic operating means communicating with said rfirst branch conduit and operatively connected with said first control means for operating the same, second hydraulic operating means communicating with said second branch conduit and operatively connected with said second control means for operating the same, a first throttle means communicating with said first branch conduit, 21 second throttle means communicating with said second branch conduit, a throttle control means for varying the throttle cross-section of said first and second throttle means, and throttle operating means operatively connected with said throttle control means and hydraulically connect-' ed with said hydrostatic transmission for operating said throttle control means in response to the pressure in said hydrostatic transmission whereby the pressure in saidifirst' and second branch conduits are proportional to the speed of said engine and to theratio of said transmission, respectively; and operator controlled means in said maincon duit for producing selected pressures in said main conduit so that in every position of said operator controlled means a diiferent rotary speed of said hydraulic motor is maintained constant and independent of the load variations of said hydraulic motor while said engine andhydraulic transmission operate at optimal efiiciency. I

2. Regulated hydraulic drive aszclaimed in claim 1 wherein said regulating apparatus includes first and second throttles having the same throttling cross section and connecting said main conduit with said first and second branch conduits, respectively.

3. Regulated hydraulic drive as claimed in claim 1 wherein said engine is a combination engine; wherein said first control means controls the admission of a fuel mixture into said combustion engine; wherein said pump is a piston pump; and wherein said second control means adjusts the length of the stroke of said pump.

4. Regulated hydraulic drive as claimed in claim 1 wherein said throttle operating means is hydraulically connected with said pump and responds to the pressure in the same.

5. Regulated hydraulic drive as claimed in claim 1 wherein said source of pressure medium is an auxiliary pump; and wherein said first and second throttle means have outlets for discharging said pressure medium.

6. Regulated hydraulic drive as claimed in claim 1 wherein said throttle control means include a throttle control member increasing the throttling cross section of said first throttle means when decreasing the throttling 7 cross section of said second throttle mean, and vice versa. 7. Regulated hydraulic drive as claimed in claim '6 wherein said throttle control member is reciprocable along a straight path between said first and second throttle means.

8. Regulated hydraulic drive as claimed in claim 6 wherein said throttle control member is mounted for throttle control member being movable by said throttle operating means into one and out of the respective other throttle opening for simultaneously reducing the throttle cross section of one of said first and second throttle means while increasing the throttle cross section of the respective other of said firstj and second throttle means.

10. Regulated hydraulicdrive as claimed in claim 1 wherein said first and second throttle means have spaced throttle openings; and wherein said throttle control means includes a throttle member mounted for movement about an axis, said throttle member having a periphery crossing said throttle openings for partly closing the same, said throttle member being turnable by said throttle operating means between angular positions for simultaneously reducing the open throttle cross section of one .of said first and second throttle openings while increasing the open throttle cross section of the respective other of said first and second throttle openings.

11. Regulated hydraulic drive as claimed in claim Ll wherein said first and second hydraulic operating means include first and second hydraulic servo motors, respectively, said first servo motor including a first cylinder communicating with said first branch conduit and a first piston connected with said first control means, and said second servo motor including a second cylinder communicating with said second branch conduit and a second piston connected with said second control means. 12.Regulated hydraulic drive as claimed in claim 1 wherein said operator controlled means includes a pressure-regulating valve communicating with said main conduit, and an adjusting meahs adapted to be operated by an operator for setting said pressure-regulating valve to maintain a selected pressure in said main conduit.

-13. Regulated hydraulic drive as claimed in claim 12 wherein said pump is, a rotary piston pump; wherein said second control means adjusts the length of the piston stroke of said pump; wherein said throttle operating means is hydraulically connected with said pump and responds to the pressure in the same; and wherein said throttle control means include a throttle control member increasing the throttling cross section of said first throttle means when decreasing the throttling cross section of said second throttle means, and vice versa.

14. Regulated hydraulic drive as claimed in claim 1 wherein said operator controlled means includes a pressure-regulating valve communicating with said main conduit, and an adjusting means adapted to be operated'by an operator for setting said pressure-regulating valve to maintain a selected pressure in said main conduit means; wherein said regulating apparatus includes first and second throttles having the same throttling cross-section and connecting said main conduit with said first and second branch conduits, respectively; wherein said engine is a combustion engine; wherein said first control means controls the admission of a fuel mixture into said com-' bustion engine; wherein said pump is a pistonpump;

wherein said second control means; adjusts the length responds to the pressure in the same; wherein said source of pressure medium is an auxiliary pump; wherein said first and second throttle means have outlets for discharging said pressure medium; wherein said throttle con trol means include a throttle control member increasing the throttling cross section of said first throttle means when decreasing the throttling cross section of said second throttle means, and vice versa; and wherein said first and second hydraulic operating means include first and second hydraulic servo motors, respectively, said first servo motor including a first cylinder communicating with said first branch conduit and a first piston connected with said first control means, and said second servo motor including a second cylinder communicating with said second branch conduit and a second piston connected with said second control means.

References Cited UNITED sTATEs PATE TS 3,175,354 3/1965 Firth etal. 19 3,533,230 10/1970 Draper 60-19 3,543,508 12/1970 Schwab 1 60-19 FOREIGN PATENTS 1,204,539 11/1965 Germany.

CARLTON R. CROYLE, Primary Examiner R. J. SHER, Assistant Examiner U.S. Cl. X.R. 417-15 

